Pseudostrabismus is a condition in which the eyes appear misaligned despite no true deviation of the visual axes. It is caused by morphological features of the face or abnormalities of the kappa angle.
Pseudostrabismus is classified into the following three types.
A retrospective population-based cohort study reported a birth prevalence of pseudostrabismus in approximately 1% of infants. Among infants diagnosed with pseudostrabismus, 4.9–9.6% later developed manifest strabismus. However, no direct causal relationship between pseudostrabismus and true strabismus has been confirmed.
It has been reported that 4.9–9.6% of infants diagnosed with pseudostrabismus later develop true strabismus. However, there is no direct causal relationship between the two; selection bias (easier screening due to continued follow-up) or misdiagnosis at the initial examination (missed intermittent deviation) may be involved.
Pseudostrabismus is not a disease and is not accompanied by subjective symptoms. Most cases involve parents who feel that their child’s eyes are turning inward (or outward) and seek medical attention.
The appearance of pseudostrabismus can be classified into three types based on the underlying facial morphology and the direction of the kappa angle.
Pseudoesotropia
Epicanthus: A crescent-shaped skin fold on the inner side of the upper eyelid covers the nasal sclera, making the eye appear esotropic.
Flat nasal bridge: Common in infants. It resolves as the nasal bone develops with growth.
Short interpupillary distance: Causes the eyes to appear close together.
Negative kappa angle: The corneal reflex is located temporal to the center of the pupil, mimicking esotropia.
Pseudoexotropia
Telecanthus: When the interorbital distance is wide, the eyes appear exotropic.
Positive kappa angle: The corneal reflex is located nasal to the center of the pupil, mimicking exotropia. Caused by temporal displacement of the macula.
Underlying diseases: Advanced retinopathy of prematurity, ocular toxocariasis, high myopia, congenital retinal fold, etc.
Pseudohypotropia and Pseudohypertropia
Facial asymmetry: One eye appears higher than the other.
Hypoglobus: The entire eyeball is displaced downward due to orbital tumor or orbital floor trauma.
Eyelid asymmetry: Eyelid retraction or ptosis creates an illusion of vertical misalignment.
The angle kappa (κ) is the angle between the pupillary axis and the visual axis. Normally, it is located about 5° nasally. When this angle exceeds ±5°, the Hirschberg test (corneal light reflex test) may suggest strabismus, but the cover test reveals no misalignment. Retinal diseases with macular displacement can cause angle kappa abnormality.
The main risk factors for pseudostrabismus are listed below.
| Risk Factor | Type of Pseudostrabismus |
|---|---|
| Epicanthal folds / flat nasal bridge | Pseudoesotropia |
| Telecanthus (increased interorbital distance) | Pseudoexotropia |
| Retinopathy of prematurity | Pseudoexotropia |
| Chorioretinal infections | Pseudoexotropia |
| Orbital tumors / orbital trauma | Pseudohypotropia / pseudohypertropia |
| Eyelid asymmetry | Pseudohypotropia / Pseudohypertropia |
Asian children often have prominent epicanthal folds (skin folds covering the inner corner of the eye), which hide the nasal sclera and make the eyes appear esotropic. As the nasal bone develops with growth, the prominence of epicanthal folds decreases.
The diagnosis of pseudostrabismus should only be made after thoroughly excluding true manifest strabismus and intermittent strabismus. In the diagnosis of esotropia, it is a principle to first rule out pseudoesotropia and organic diseases.
Pseudoesotropia is not true strabismus, so active treatment including surgery is unnecessary. Management focuses on the following three points:
This is necessary. Since some infants diagnosed with pseudostrabismus later develop true strabismus, a follow-up visit within 6 to 12 months is recommended. Particularly in cases with high hyperopia, there is a risk of accommodative esotropia, making regular follow-up important.
The mechanisms of pseudostrabismus are broadly divided into facial anatomical features and abnormalities of the angle kappa.
Epicanthal folds are crescent-shaped skin folds extending from the inner upper eyelid toward the nose, covering the nasal sclera. This makes the cornea appear displaced nasally, giving the appearance of pseudoesotropia. In infants, a flat nasal bridge enhances this effect. As the nasal bone develops with growth, the prominence of epicanthal folds decreases, and in many cases, the appearance of pseudoesotropia resolves by 2 to 3 years of age.
Normally, when the fovea fixates on a target, the line of sight passes approximately through the center of the pupil. The angle kappa (the angle between the pupillary axis and the visual axis) is usually about 5°, and the corneal reflex is located slightly nasal.
When the angle kappa exceeds ±5°, the following pseudostrabismus occurs:
In pseudostrabismus due to angle kappa abnormality, the Hirschberg test may appear as strabismus, but the cover test and alternate cover test reveal no strabismus at both near and distance. Stereopsis is also good, and surgery is not indicated.
Pseudoesotropia due to epicanthal folds often resolves by 2 to 3 years of age as the nasal bridge grows. On the other hand, pseudostrabismus due to positive or negative angle kappa abnormalities or other static facial morphology persists. In either case, there is no impact on visual function.
